Ignorance is literally lack of knowledge. In modern usage, however, it's become an insult. To be called ignorant is to be described as uneducated, or too stupid to comprehend the facts of a subject.To say someone is 'acting in ignorance' is a statement which effectively describes the nature of the action in advance. Certain types of social or cultural behavior may be described as ignorant with other qualifiers like 'boorish'.